The objectives of the proposed research are the synthesis and biologic evaluation of imaging agents for the detection and differential diagnosis of disorders, including carcinoma, of the pancreas, adrenals, breast and brain. Successful treatment of these disorders relies upon early detection; however, this is seldom achieved by scintigraphic imaging techniques because of shortcomings associated with the radiopharmaceutical. The development of new organic radiodiagnostic agents which possess greater organ or disease selectivity will provide more informative scintigraphic images, thus enabling the early detection of the suspected pathophysiology and improving the prognosis of the patient. Our recent experience in selenium chemistry has indicated that the approach with the highest probability of success involves the preparation of analogs of the appropriate organ or disease selective drugs in which the selenium is either disubstituted or located in an aromatic ring. This will provide for greater isoelectronic and isosteric analogy to the parent drug and for greater stability to metabolic degradation. We propose that selenium containing analogs of the following classes of compounds be prepared and evaluated as potential imaging agents: aromatic amino acids for the pancreas, adrenal Corticosteroid enzyme inhibitors for the adrenal, estradiol for breast cancer, levamisole for the immune system, and CNS active drugs for the brain. The prepared substances will be evaluated in animals to determine their pharmacokinetics, biologic distribution, toxicity and ultimate fate. The stability of these agents will be investigated by double labeling (14C or 3H and 75Se). Any radiopharmaceutical emerging from this work which exhibits potential for effective imaging in man will be considered for evaluation in a clinical trial.